Strugling to Afford sychiatric Medicines

I have been facing mental health issues and recently visited the Psychiatry Department at a Government Hospital. The doctor prescribed some medicines, but these are not available in the hospital, so I have to buy them from outside. I approached a charitable trust for help, and they agreed but asked for an expenditure letter from the treating Psychiatric doctor. However, when I requested the letter, the doctor said they can’t provide it for OPD patients, as expenditure letters are only issued for admitted patients. Now, the charitable trust says they can't help without the expenditure letter, and I'm stuck in between. The medicines are expensive, and I can't afford to buy them from my pocket. Since psychiatric medications need to be taken for a long time and are not available in Jan Aushadhi, in generic form, or at the hospital—and I’ve already tried all available alternatives—how can I get help from the charitable trust?